1. Title of the Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine, and more relates to make the image forming apparatus compact.
2. Description of the Related Art
In image forming apparatus known as a printer, a copying machine, and a facsimile machine, which employ electrophotographic systems, images are formed as follows: that is, after light is irradiated onto an image carrier such as a photosensitive drum which has been uniformly charged by electrostatic latent image forming unit to acquire electrostatic latent images, toners are applied to the electrostatic latent images so as to be visualized by developing unit. Then, for example, a plurality of toner images are multiplex-transferred onto an intermediate transfer member. The multiplexed toner image is transferred onto a recording medium (such as a paper) so that the toner image is fixed on the recording medium.
In related art, such a technical idea is known (refer to, for example, JP-A-11-109767 at pages 4 to 5, FIG. 1). That is, a rotary type developing apparatus is provided in proximity to a photosensitive drum, which holds four colors (yellows magenta, cyan, and black) of developing devices functioning as developing device along a circumferential direction of a rotary member. Toner images which are sequentially formed by this rotary type developing apparatus are transferred onto a transfer belt in a multiplexing manner. In the image processing apparatus of a system as indicated in JP-A-11-109767, when a full color image is outputted, every time the transfer belt is rotated by one turn, a yellow-color toner image, a magenta-color toner image, a cyan-color toner image, and a black-color toner image are primary-transferred onto this transfer belt. The four color toner images are sequentially overlapped with each other on the transfer belt. Then, the toner image is secondary-transferred onto a paper by employing a secondary transfer roller at a secondary transfer position from a portion where all of these four color toner images have been overlapped with each other.
At this time, in JP-11-109767, such a layout is designed in which the distance between the primary transfer portion and the secondary transfer portion becomes long in order that the tip portion of the toner image is not reached to the secondary transfer portion before the primary transfer operation as to such a paper whose transport length is long is completely accomplished. Other than JP-11-109767, another technical idea is known (refer to, for example, JP-9-90779 at pages 3 to 5, FIGS. 1 and 3). That is, in a color image forming apparatus in which a toner image formed on an image carrier is primary-transferred to an intermediate transfer member, and then, the toner image on the intermediate transfer member is secondary-transferred to a transfer medium (such as a paper), a distance defined from a primary transfer position up to a secondary transfer position is set to be longer than the maximum length of the transfer member. As previously explained, since the distance defined from the primary transfer position up to the secondary transfer position is set to be longer than the maximum length of the transfer material, it is possible to avoid that the primary transfer operation is carried out during the secondary transfer operation. Thus, the speed variation occurred when the transfer material rushes into the secondary transfer position can be prevented.
Furthermore, another image forming apparatus which employs the following system has been proposed (refer to, for instance, JP 2002-341706 at pages 3 to 5, FIG. 1). In this image forming system, in order that a plurality of color images are superimposed with each other on an intermediate transfer belt and the superimposed color image is transferred so as to obtain a color image, a recording medium storage unit is arranged at a lower side of this image forming apparatus, a transfer material is transported along a substantially vertical direction, and after an image is formed on this transfer material, this transfer material is ejected to an ejection unit provided on an upper side of this apparatus. In the layout described in JP 2002-341706, an intermediate transfer belt is arranged on the upper side of the rotary developing apparatus, and the ejection tray is provided above this intermediate transfer belt.
In the technical ideas described in the patent JP-11-109767 and JP-9-90779, however, since the distance between the primary transfer position and the secondary transfer position is very long, for instance, a time duration until the secondary transfer operation is carried out after the primary transfer operation has been carried out is prolonged, and thus, a so-called “throughput time” becomes very long. Furthermore, in the technical ideas described in JP-11-109767 and JP-9-90779, the distance defined between the primary transfer position and the secondary transfer position is long, so that the image forming apparatus becomes bulky.
In JP2002-341706, a solving device with respect to entering of the transfer material into the secondary transfer position is not completely disclosed. Shocks occurred when the transfer material is entered into the secondary transfer position cannot be prevented. A so-called “smear” which is caused by such a phenomenon that the transfer material scrapes the surface of the intermediate transfer belt cannot be avoided.